The present invention relates to the treatment of sludge from wastewater treatment facilities.
Sludge is composed of solid and dissolved material in a liquid matrix. Important factors in the digestion process are the rate and extent of sludge digestion, and the extent to which water can be removed from the digested sludge. Sludge solids include both organic and inorganic material. Sludge digestion reduces the amount of organic solids in the sludge, but has no effect on the inorganic component. The biodegradable organic matter in the sludge is used as food by aerobic microorganisms (mostly bacteria) during aerobic sludge digestion. The products of this biodegradation are carbon dioxide, water and bacterial cells. As long as this food source and oxygen are readily available the aerobic bacteria continue to feed and multiply. As the removal of the non-living organic material originally present in the sludge nears completion, the microbial populations"" growth rates slow until the death rate eventually exceeds the birth rate. Much of the dead bacterial cell material is then consumed by the survivors and the sludge is xe2x80x9cdigestedxe2x80x9d.
The digested sludge can be de-watered by allowing it to stand under quiescent conditions, so that the solids settle and a layer of liquid supernatant forms above the settled sludge. This liquid is returned to the wastewater treatment plant for further treatment, and the de-watered sludge is trucked to its ultimate disposal point. Clearly, the more liquid that can be separated from the sludge at this stage, the lower the trucking costs will be.
While many methods have been suggested to aid in de-watering of digested sludge, only marginal improvement has been achieved.
It is an object of the present invention to provide a method to allow an increase in the amount of water that can be removed from the sludge.
It is a further object of the present invention to provide a method for reducing plant operating cost in a sewage treatment plant.
According to one aspect of the present invention there is provided a method for the treatment of sludge comprising the step of applying to the sludge a biologically effective amount of a composition containing a lignosulfonate and sludge digesting microbes.
According to a further aspect of the present invention there is provided a method for the suppression of ordours in a bolding tank containing organic waste matter, the method comprising the step of adding to the organic waste material a biologically effective amount of a composition containing a lignosulfonate and organic material digesting microbes.
According to a further aspect of the present invention in a method for the treatment of sludge in a sewage treatment plant wherein the sludge is subjected to an aerobic treatment, there is provided the improvement comprising the step of adding to the sludge during the aerobic treatment a biologically effective amount of a composition containing ammonium lignosulfonate and sludge digesting microbes.
Lignins are a natural complex polymer which are generally produced as a co-product of the paper industry, the lignins being separated from the trees by a chemical pulping process. Lignosulfonates are also known as ligninsulfonates and sulfite lignins are products of sulfite pulping. Other delignifying technologies may include the use of an organic solvent or high pressure steam treatment to remove lignins from plants.
As aforementioned, lignin is a very complex natural polymer, the exact chemical structure not being known. Physical and chemical properties can differ depending on the extraction technology. Lignosulfonates have typically been used for their dispersing, binding, complexing and emulsifying properties. Lignins have been used for many years and extensive studies have been done to test lignin impact of the environment. To-date, lignins have been shown to be safe and non harmful to plants, animals and aquatic life when properly manufactured and applied. Furthermore, lignosulfonates have been found to be essentially non toxic and non irritating.
Surprisingly, it has been found that the use of the lignosulfonate with microbes is very efficient and cost effective way of reducing sludge volume.
The composition used in the present invention will preferably use microbes selected from those known to those knowledgeable in the art as being suitable for use in the treatment of sludge. As such, many such microbes have been used and are suitable for the practice of the present invention. Typical of such microbes, although the invention is not limited thereto, are those from the family Bacillus.
The microbial content of the composition may vary depending upon the material being treated and the results which are desired. It suffices to say that those knowledgeable in the art, given the teachings of the present invention, would be able to select the bacteria and amount thereon. Generally, it is preferred that the composition contain between 0.5% and 5% of a bacterial concentrate. Typically, such bacterial concentrates have a viable bacteria content (CFU) in the billions of organisms per gram. As such, the composition will have a microbial content of greater than 50,000 CFU per gram.
Preferably, the composition contains between about 80% to about 91.5% by weight of ammonium lignosulfonate, between about 8% and 15% by weight of a pH adjusting agent, and between about 0.5% and about 5% by weight of a concentrated microbial product. When the composition is utlized as a liquid, the dry composition may be mixed with water in a weight volume ration (grams/liters) of between 2:1 and 20:1.
The composition may be applied directly to the sludge and mixed therewith and/or could be applied as a liquid if so desired. Naturally, any other desirable material may be employed in the composition.
The composition can be utilized in commercial sludge treating systems or plants. However, the present invention also provides, in one particular embodiment, for the treatment of holding tanks. In particular, the present invention can be used in the treatment of holding tanks for recreational vehicles and the like and in the use of portable toilets.
One advantage of the present invention has been found to be a substantial odor reduction or suppression without the use of fragrances. This presents a substantial advantage in the treatment of holding tanks and portable toilets.
As aforementioned, other ingredients can be added to the composition. Thus, although the present invention does achieve an odor suppression, if a particular fragrance is desired, then it could be added to the composition. Similarly, colorings such as dyes to provide a desired color for the composition can be incorporated.
The composition of the present invention can be used in treating holding tanks such as are encountered with recreational vehicles and for treating the sewage in portable toilets. At present, formaldehyde is widely used as a treatment for the suppression of odours. Naturally, the use of formaldehyde is undesirable from an environmental point of view. The composition of the present invention can achieve odour suppression equal to that achieved with formaldehyde while also providing a sludge digestion.